[jjj]

1/8" NPT is no where near 1/8" Impearal...

1/8" NPT ( National pipe thread (usa). )
is nearer 1/4" impearal. ( 6mm )

 

[jjj]

The lines used in USA ( Example 1/8") will be true 1/8" outside ( 2.5mm)

Becarful trying to size NPT ( USA ) against BSP ( UK ) they are different..........Alot......

( 1/8" NPT about the size of 1/4" BSP )

BSP = "British standard pipe"

 

[jjj]

If you are going to tap your own thread. you can use whatever fittings u like..
still may have problem at gauge end , if using USA gauge.

 

[jjj]

should be i haven't tried..
thats neat way to install line to gauges...
4 less t-pieces in the system ( fbss ).....

Top marks to 216..